System and method for cleaning fracking sand

ABSTRACT

According to at least one exemplary embodiment, a system for cleaning fracking waste slurry containing water, sand, and organic matter may include a slurry sump, separator, dewatering screen, water tank, surge hopper, and a sand cleaner. The sand cleaner may further include a rotary retort furnace which may both dry the sand and oxidize any organic matter. The cleaning system may recycle the water used by returning it to the truck that brought the waste slurry. Further, the dried and cleaned sand produced by the system may be suitable for re-use or non-hazardous disposal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/839,952 filed Jun. 27, 2013 and entitled SYSTEM AND METHOD FOR CLEANING FRACKING SAND, the entire contents of which are hereby incorporated by reference.

BACKGROUND

Hydraulic fracturing is an increasingly-used method to extract natural gas and oil from the earth. Hydraulic fracturing involves the introduction of a high-pressure mixture of water and sand and/or chemicals into faults or cracks in rock structures, such as shale. The mixture is pumped through a well deep underground and the pressure creates larger fractures allowing for the release of the gas or petroleum. After achieving its purpose, the mixture is then extracted from the well as waste slurry containing water, sand, and some organic matter extracted from the ground. This waste slurry is subject to strict regulations, most notably by the U.S. Environmental Protection Agency, and therefore slurries containing certain contaminants can be immensely difficult and expensive to dispose of.

A method of cleaning the sand in the waste slurry that is both effective and environmentally friendly is highly desirable. Washing and drying systems for sand may tend to use wash water, and produce a quantity of dust. It would be advantageous to recycle at least part of the wash water, and thereby to reduce overall water consumption as compared to using only fresh water. Further, an effective method for oxidizing the organic matter contained in the slurry is necessary to produce clean sand. The cleaned sand could then be re-used in the same or another fracking well, or could be disposed of in a non-hazardous manner.

SUMMARY

According to at least one exemplary embodiment, a system for cleaning fracking waste slurry containing water, sand, and organic matter may include a slurry sump, separator, dewatering screen, water tank, surge hopper, and a sand cleaner. The sand cleaner may further include a rotary retort furnace which may both dry the sand and oxidize any organic matter. The cleaning system may recycle the water used by dispensing it into a storage container, a truck that brought the waste slurry, or in any other way. Further, the dried and cleaned sand produced by the system may be suitable for re-use or non-hazardous disposal.

BRIEF DESCRIPTION OF THE FIGURES

Advantages of embodiments of the present invention will be apparent from the following detailed description of the exemplary embodiments. The following detailed description should be considered in conjunction with the accompanying figures.

Exemplary FIG. 1 is a schematic diagram of an embodiment of a slurry sand cleaning system.

Exemplary FIG. 2 is a top-down view of an embodiment of a slurry sand cleaning system, showing a possible orientation of the components of the system.

Exemplary FIG. 3 is a side view of an embodiment of a slurry sand cleaning system, showing a possible orientation of the components of the system.

Exemplary FIG. 4 is a side view of the sand cleaner component of an embodiment of a slurry sand cleaning system.

Exemplary FIG. 5 is a side view of an exemplary embodiment of a sand cleaning system.

Exemplary FIG. 6 is a side view of an exemplary V-bottom slurry tank.

Exemplary FIG. 7 is a side view of an exemplary retort furnace natural gas tumbler.

Exemplary FIG. 8 is a side view of an exemplary twin auger conveyor pre-heat tank hopper.

Exemplary FIG. 9 is a side view of an exemplary dry bulk hopper.

DETAILED DESCRIPTION

Aspects of the invention are disclosed in the following description and related drawings directed to specific embodiments of the invention. Alternate embodiments may be devised without departing from the spirit or the scope of the invention. Additionally, well-known elements of exemplary embodiments of the invention will not be described in detail or will be omitted so as not to obscure the relevant details of the invention. Further, to facilitate an understanding of the description discussion of several terms used herein follows.

As used herein, the word “exemplary” means “serving as an example, instance or illustration.” The embodiments described herein are not limiting, but rather are exemplary only. It should be understood that the described embodiment are not necessarily to be construed as preferred or advantageous over other embodiments. Moreover, the terms “embodiments of the invention”, “embodiments” or “invention” do not require that all embodiments of the invention include the discussed feature, advantage or mode of operation.

According to at least one exemplary embodiment, a system for cleaning hydraulic fracturing waste slurry may include a slurry sump, separator, dewatering screen, water tank, surge hopper, and a sand cleaner. The sand cleaner may further include a rotary retort furnace which may both dry the sand and oxidize any organic matter. The cleaning system may recycle the water used by dispensing it into a storage container, a truck that brought the waste slurry, or in any other way. Further, the dried and cleaned sand produced by the system may be suitable for re-use or non-hazardous disposal.

Exemplary FIG. 1 shows a schematic diagram of an embodiment of cleaning system 100. Cleaning system 100 may include a slurry sump 110, a separator 120, a dewatering screen 130, a water tank 140, a surge hopper 150, and a sand cleaner 160. The initial waste slurry to be cleaned may be provided by means of a truck 10. Alternatively, the initial waste slurry may be provided by another vehicle, such as a train, or may be provided directly from the well in which the slurry was used, or as desired.

Referring generally to exemplary FIGS. 1, 2, and 3, waste slurry from a hydraulic fracturing, well containing a liquid carrier, sand, and organic matter may be transported to be cleaned in a truck 10. The liquid carrier may be, for example, water. The sand may be of any sand suitable for use in hydraulic fracturing. Though not intended to be limiting, exemplary sand may include Utica White frac sand from Illinois. Mesh sizes for the sand may be, but are not limited to: 100, 16/30, 20/40, 12/20, 80/40, 30/50, 40/70, 80/120, and 30/60 mesh. According to some embodiments, truck 10 may be a vacuum truck. Alternative delivery mechanisms such as from another type of vehicle or directly from the well are also envisioned; however, here only a truck will be referred to for clarity. Waste slurry may be pumped from truck 10 into slurry sump 110 by way of hoses or by any other means, as desired. The rate of waste slurry pumping from truck 10 to slurry sump 110 may vary depending on the capacity of the cleaning system. In an exemplary embodiment, the rate of waste slurry pumping from truck 10 to slurry sump 110 may be any rate up to 300 gallons per minute. Slurry sump 110 may temporarily store slurry to achieve a desired throughput for the rest of cleaning system 100, if desired. Waste slurry may then be pumped out of slurry sump 110 by means of slurry pump 112. Slurry pump 112 may pump waste slurry to separator 120.

Separator 120 may have the ability to functionally separate the waste slurry in a lighter portion of excess water without particulate matter in it and a denser portion containing partially dewatered waste slurry. Separator 120 may be, for example, a hydrocyclone, a centrifuge, or as desired. Separator 120 may have two exits: an underflow 122 and an overflow 124. The partially dewatered waste slurry may exit separator 120 at underflow 122 and travel to dewatering screen 130. The excess water may exit separator 120 at overflow 124 and travel to either slurry sump 110 or water tank 140.

Dewatering screen 130 may vibrate and further dewater the waste slurry. Excess water extracted by dewatering screen 130 may flow back to slurry sump 110. Dewatering screen 130 may dewater waste slurry to convert it into a drip-free hydraulic fracturing sand cake (“cake”) containing at least about 85% solids and less than about 2% combustible organics.

Excess water from separator 120 may flow either back to slurry sump 110 or to water tank 140, as desired. A valve may be used to determine the direction of the water flow to maintain a desired water level in slurry sump 110. Water in water tank 140 may be pumped back onto truck 10 for returning to the fracking well site or for disposal, as desired. Alternatively, water in water tank 140 may be recycled or disposed of onsite.

Cake exiting dewatering screen 130 may be transported to surge hopper 150. Cake may be transported by conveyer belt 132, or as desired. Surge hopper 150 may allow cake to flow along feeder 152 into sand cleaner 160 at a desired rate. Surge hopper 150 may also serve as a temporary storage for cake, if desired.

Referring now to exemplary FIG. 4, cake from feeder 152 may enter sand cleaner 160 through screw feeder 162. Screw feeder 162 may ensure a constant flow of cake into sand cleaner 160. From screw feeder 162, cake may enter rotary retort furnace 164. Furnace 164 may heat cake to a high temperature, for example between about 1,200° F. and about 1,500° F., which may completely dry cake converting it back to dry sand. Further, furnace 164 may rotate, causing sand to be mixed and cascaded for even processing. Furnace 164 may have an annular cavity 166 between its outside and inside surfaces. Burners may be fired into the annular cavity 166, providing for indirect heating of the cake and sand.

Sand cleaner 160 may further include an air valve. Air valve may be coupled directly to screw feeder 162 or to furnace 164. Air valve may allow for the control of airflow in furnace 164, this airflow may in turn control both the drying of the cake into sand and the oxidization of organic matter in the cake/sand material. In one embodiment, airflow may be adjusted to provide for an oxygen concentration between about 5% and about 10% within furnace 164 at initial startup. Air valve may be either manual or automatically adjustable, as desired.

After passing through sand cleaner 160, the processed sand may be dry and free of any organic content. Processed sand may be suitable for re-use, for example in a fracking operation or other uses, or non-hazardous disposal.

Smaller-scale and larger-scale embodiments of the invention are both envisioned. According to some embodiments, an embodiment of the disclosed cleaning system may be able to process 1,500 barrels of waste slurry per day. In addition, according to one exemplary embodiment, the waste slurry may contain up to about 30% solid matter before processing.

As shown in exemplary FIG. 5-9, some embodiments may include a V-bottom slurry tank 210, a dry bulk hopper 240, a twin auger conveyor pre-heat hopper 230, and a retort furnace natural gas tumbler 220. Retort furnace natural gas tumbler 220 may be configured such that cake is fed into the tumbler by a belt or auger. In an exemplary embodiment, cake may be transferred to the tumbler from twin auger conveyor pre-heat hopper 230. The tumbler may be substantially tubular and may be sloped such that gravity causes the sand to travel through the tumbler and fall out the end opposite the feeder. Cake or waste sand may be deposited onto the interior surface of the tumbler tube. The tumbler may rotate, causing the sand to mix and spread as it slides down the rotating tube. A barrier may be disposed within the tumbler tube. The barrier may substantially form an inner tube within the tumbler tube. The barrier may or may not be continuous. The barrier may be made of substantially heat resistant, heat reflective, or heat dispersing material. The waste sand or cake may travel along the interior of the tumbler tube outside of the barrier. A heating element may be disposed within the barrier tube, such that the barrier is between the heating element and the sand. The barrier may increase or decrease the heat exposure of the sand and may disperse the heat evenly. In at least one exemplary embodiment, the heating element may be a burner configured to project heat into the tumbler tube. The burner may be disposed at the end of the tube opposite the feeder. As the sand travels down the tumbler tube, it may be evenly heated and cleaned. Heat may be radiated from the burner, the barrier, and the tumbler tube itself, causing for uniform heating and cleaning. The dry, cleaned sand may fall out of the tumbler tube and be collected for disposal or reuse.

The foregoing description and accompanying figures illustrate the principles, preferred embodiments and modes of operation of the invention. However, the invention should not be construed as being limited to the particular embodiments discussed above. Additional variations of the embodiments discussed above will be appreciated by those skilled in the art.

Therefore, the above-described embodiments should be regarded as illustrative rather than restrictive. Accordingly, it should be appreciated that variations to those embodiments can be made by those skilled in the art without departing from the scope of the invention as defined by the following claims. 

What is claimed is:
 1. A system for cleaning a sand slurry, the sand slurry comprising at least sand and a liquid, comprising: a separator; a dewatering screen; and a sand cleaner; wherein the separator is configured to separate the sand slurry into a first portion and a second portion, the first portion comprising excess liquid substantially free of particulate matter, and the second portion comprising partially concentrated slurry, wherein the dewatering screen is configured to remove the liquid from said second portion until it contains at least about 85% solid matter and less than about 2% combustible organic matter, and wherein the sand cleaner includes a furnace, said furnace configured to heat said second portion to a temperature sufficient to remove substantially all liquid and oxidize substantially all organic matter contained in said second portion.
 2. The system of claim 1, further comprising a slurry sump.
 3. The system of claim 2, further comprising a slurry pump, the slurry pump configured to pump sand slurry out of the slurry sump.
 4. The system of claim 3, further comprising a water tank.
 5. The system of claim 4, wherein the slurry sump, water tank, and separator are in fluid communication with each other, wherein the slurry sump may be configured to receive the sand slurry from an outside source and the separator may be configured to receive the sand slurry from the slurry sump, and wherein both the water tank and the slurry sump are configured to receive the first portion from the separator.
 6. The system of claim 1, further comprising a surge hopper.
 7. The system of claim 1, wherein the separator is a hydrocyclone.
 8. The system of claim 1, wherein the furnace is configured to heat said second portion to a temperature between about 1,200° F. and about 1,500° F.
 9. The system of claim 1, wherein the system is configured to receive the sand slurry from a truck tank.
 10. The system of claim 1, wherein the system is configured to pump the first portion to a truck tank.
 11. The system of claim 1, wherein the furnace is a rotary retort furnace.
 12. The system of claim 1, wherein the furnace is configured to control the oxygen content of the gases inside the furnace.
 13. The system of claim 12, wherein the furnace is configured to maintain the oxygen content of the gases inside the furnace between about 5% and about 10%.
 14. A method for cleaning a sand slurry and producing cleaned sand, the sand slurry comprising at least sand and a liquid, comprising: receiving the sand slurry from an outside source; separating the sand slurry in a separator into a first portion and a second portion, wherein the first portion comprising excess liquid substantially free of particulate matter, and the second portion comprising partially concentrated slurry; removing the liquid from said second portion until it becomes a cake, said cake containing at least about 85% solid matter and less than about 2% combustible organic matter; and heating the cake in a furnace to a temperature sufficient to remove substantially all liquid and oxidize substantially all organic matter contained in said cake.
 15. The method of claim 14, wherein the cake is heated to a temperature between about 1,200° F. and about 1,500° F.
 16. The method of claim 14, further comprising controlling the oxygen content of the gases inside the furnace.
 17. The method of claim 16, wherein the oxygen content of the gases inside the furnace is maintained between about 5% and about 10%.
 18. The method of claim 14, further comprising controlling the rate of flow of the cake into the furnace.
 19. The method of claim 14, further comprising pumping the first portion to a holding container.
 20. The method of claim 19, wherein the holding container is one of a water tank, a slurry sump, or a truck. 